Apparatus for sampling pulp



Patented Oct. 28, 1952 APPARATUS FOR SAMPLING PULP Sigbjiirn Paul Herbert Ebbinghaus Holgersson, Ockelbo, Mac Sigurd Rudberg and David Rune Rydbergstorvik, Sweden I 3 Application November 2 1948; Serial No. 57,972 f Y In Sweden November 21, 1947 In cooking chemical pulp the rate of decomposition of the pulp contained in the digester is rapidly increased at the end of the cooking period and as the quality of the pulp produced is highly dependent on this rate of decomposition it is of 1 Claim. (Cl. 73-423) great importance to stop the cooking at the v proper time.

In the sulphite process the proper time for stopping the cooking period is generally determined means of analyses of lye samples tapped from the digester, while in the sulphate process where generally the cooking of the pulp is performed'considerably faster than in the'sulphite method the cooking is controlled in accordance with predetermined diagrams of pressure and temperature and is stopped after a predetermined time. However, both these methods permit varying rates of decomposition as the cooking liquor added and the quality and quantity of the wood can never be maintained exactly constant from cook to cook and therefore the stopping of the cooking often occurs too early or too late.

It has also been proposed to avoid this inconvenience by providing the digesters with sampling cocks through which small amounts of the pulp itself are withdrawn and analyzed. Thus samples have been taken of the pulp located immediately adjacent or close to the digester wall. This method has not proved to be reliable in that the samples withdrawn are not representative of the whole quantity of the pulp in the digester.

By careful research we have now found that the liquor within the digester doesnt circulate at substantially the same speed in all points in the digester, as was previously assumed to be the case. Thus in the layer adjacent th digester wall the speed of circulation of the liquor is considerably higher than further into the center of the digester. As more rapid circulation will cause more rapid decomposition, the pulp inthe layer close to the wall will be cooked faster and this might be the explanation for the wrong results obtained by the sampling methods hitherto used.

This invention is accordingly'based on the discovery mentioned above and comprises the methed of inserting a sampling tube through the digester wall and withdrawing pulp samples at different distances from said wall. In its fully inserted position the tube should be long enough to extend to or beyond the center of the digester. According to a preferred mode of operation the tube is slowly pushed inwardly towards the center of the digester and simultaneously a pulp sample is withdrawn continuously and is caused to run out in the form of a string onto awire web, and thus we obtain a reproduction or; the appearance of the pulpin a sectionof the digester. a

According to the invention it is now possible to determine the rate of decomposition'of the pulp with verygreat exactness .and the cooking can. be stopped at the critical time. Moreover the reliable control makes .it possible to carry out the cooking more rapidly'than before. As an 1 example it will be mentioned that without any inconvenience a prior cooking'time of 1'7 hours may be reduced to 13-14 hours. Thus we obtain a smoother quality of pulp as well as a greater plant capacity per unit time. I

The invention also comprises adevice which is useful in carrying out. the method described above. Two embodiments of said device are shown in the accompanying drawings wherein:

Fig. 1 shows in longitudinal section a view of a testing apparatus inserted in the wall of a digester.

Figs. 2 and 3 show two details of the apparatus in Fig. l on a larger scale.

In the drawings 5 designates a portion of a digester wall through which a tube 6 is inserted.

A packing box I attached to the wall 5 on its outer side surrounds the tube and provides a leakproof seal between the tube and the wall. The outer end of the tube 6 is suspended in a bracket 8 by means of a slide 9 fixed to the tube and slidable along said bracket. A toothed wheel I0 is rotatably supported on the slide and engages a rack H mounted in longitudinal direction on the bottom edge of the bracket. By rotating the toothed wheel It] by means of a crank l2 the tube may be advanced intothe digester or withdrawn therefrom. To preventthe tube 6 from slipping out of thepacking box 1 the bracket 8 is bent downwardly atits outer end, as seen at.|3 in Fig. 1.

The inner end of the tube 6 is'covered by a disk M (Fig. 2) which is smooth on the outside I and provided with one or moreholes l5 through which the pulp is adapted to enter the tube.

is mounted in contact with the smooth outer side of the disk M to prevent clogging of the hole A. rotatable sharp edged scraper l6 (Figs. 2 and 3) pulp is withdrawn from the tube 6 through a branch 20 inserted adjacent the outer end of the tube 6. Branch 20 is closed by a valve 2|.

In withdrawing samples the tube 6 is inserted into the digester whereupon the valve 2| is opened. The lye and pulp flow through the hole l and out through the valve 2|. When coarse pulp pieces tend to obstruct the hole they are scraped off by rotating: the scraper I6. To prevent pulp pieces from lodging in the hol itself it is preferable to have the latter sharp-edged and increasing in width inwardly. The pulp is forced through the tube by a pressure differential due to the existence of atmospheric pressure exteriorly of and superatmospheric pressure in, teriorly of the digester.

In operating the embodiment above described the pulp sample is obtained in somewhat defibered form. Withdrawing of samples may be efiected in any desired distance from the digester W l o t c nte o the d g ster o fu I is also possible t use several devices according he n ent on. placed sui b l ca ons around the digester,

It is obvious that the apparatus constituting the invention may be constructed in ways other than described above. The essential feature is that samples are withdrawn from one or more places ata Dl'fidetermined distance from the digester wall, 1. e., from places where the rateof de si n of the lp s rm- We claim: 7

An apparatus for withdrawing Samples from 4 a digester in cooking chemical pulp, comprising a sampling tube slidably extending through the digester wall, said tube having an outlet valve adjacent its outer end, a disc covering the inner end of said tube, said disc having a smooth outer surface and being provided with at least one opening to permit entry of the pulp into said 1 tube, a scraper arranged to rotate in contact with the outer surface of said disc, a packing box at the outer end of the tube and a rotatable shaft passing through said packing box, extending coaxially through the tube, and connected to said scraper to rotate the same.

s Jfo'RN PAUL HERBERT EB'BINGHAUS HOLGERSSON. MAC SIGURD RUDBERG. DAVID RUNE RYDBERG.

REFERENCES CITED The following references are of record in the file of this patent: ..1

UNITED STATES PATEN S 

